Digital Radiography (DR) detectors directly transform received exposure energy to digital image data. These detectors commonly contain an array of light sensitive picture elements, or pixels, arranged in a matrix of rows and columns and a scintillator, consisting of a material, such as gadolinium oxisulfide, Gd2O2S:Tb (GOS) or cesium iodide, that absorbs x-rays incident thereon and converts the x-ray energy to visible light photons. The array of light sensitive elements can be any type of solid state sensor, such as a flat panel detector, a charge-coupled device, or CMOS detector. The light sensitive material converts the incident light into electrical charge that is stored in the internal capacitance of each pixel. The magnitude of the stored electrical charge is related to the intensity of the excited light, which is, in turn, related to the intensity of the incident x-rays. The radiation image exposures captured on radiation-sensitive layers are converted, pixel by pixel, to electronic image data that is then stored in memory circuitry for subsequent read-out and display on suitable electronic image display devices.
Much like video sensors and other types of two-dimensional solid state image detectors, DR detectors include several thousands of picture elements, or pixels, which inevitably differ in their characteristics.
Medical digital x-ray images are commonly corrected for pixel-to-pixel variations in dark current and sensitivity. These correction operations can be referred to as offset (or dark) corrections and gain corrections (compensations). Prior to the corrections, offset maps and gain maps (e.g., two-dimensional images characterizing the aforementioned pixel-to-pixel variations) are generated in an offset calibration operations and gain calibration operations. In addition, a defect map can be made for every detector that contains the locations of pixels with abnormal properties. These abnormal or defective pixels are corrected using the values of adjacent good pixels in a defect correction operation. Thus, each detector manufactured has a unique set of calibration maps that are created at the factory. The set of initial or factory calibration maps can be updated each time a detector is subsequently calibrated by the user (e.g., field calibration).
Calibration procedures require radiology staff time and attention and each calibration reduces the overall utilization time of a DR detector.
Consequently, there is a need for improved calibration and correction procedures for DR detectors.